The present invention relates to a hydraulic power booster arrangement, in particular for actuation of master cylinders in vehicular brake systems.
There are already known arrangements of this type, wherein two cylinder bores arranged substantially in parallel in a housing terminate in a pressure chamber, wherein a booster piston is guided in the first cylinder bore while a brake valve is inserted in the second cylinder bore for the control of pressure fluid communications from the pressure chamber to a pressure source or to an unpressurized return reservoir, wherein a multipart lever actuation mechanism is provided to govern the brake valve, such mechanism having a first lever which is stationarily supported in the housing and tiltable by a pedal-actuatable push rod or similar operating element and having a second lever which is supported rotatably at the first lever and bears against the booster piston and the brake valve.
A hydraulic booster imcorporating the features mentioned hereinabove is known from German patent specification No. 15 80 690, wherein the first lever is of U-shaped design and its bending point is placed in the area of the point of support at the push rod. The first lever is bifurcated in the area of its bending point so that a bolt extending normal to the actuating direction and mounted at the push rod is guided in the slot slidably in longitudinal direction. The open ends of the first lever are stationarily supported on the housing by means of a screw inserted laterally into the housing. Arranged between the legs of the U-shaped lever is a second lever which engages the brake valve, on the one hand, and the booster piston, on the other hand. The two levers are pivotally interconnected approximately at their central regions.
In response to an actuating force acting on it, the push rod and the bolt connected therewith will first perform a short travel during which the first lever is tilted in one direction about its stationary point of support. Simultaneously, also the connecting point between the levers will tilt. Since the actuating forces of the booster piston are substantially greater than the control forces of the brake valve, this tilting movement has as a consequence that the second lever is angularly displaced in the opposite sense relative to the first lever and actuates the brake valve. Now, pressure fluid is introduced through the brake valve into the pressure chamber, resulting in displacement of the booster piston in the actuating direction. This displacement causes the second lever to turn back until the relative position which prevailed prior to the actuating has be reestablished between the levers. Upon discontinuance of the actuating force, the relative motions described above will be reversed until the inactive position is established again in which the pressure chamber communicates with the unpressurized return reservoir.
A particular disadvantage of the just described hydraulic power booster arrangement is that the assembly of the lever actuation mechanism requires great effort. First, it is necessary to put the U-like bent lever around the push rod while making sure that the bolt formed at the push rod slides into the guiding slot provided for it. Then the free ends of the U-shaped levers have to be secured by the screw extending laterally into the pressure chamber. During this process, there is only a very limited access from the outside to the free ends of the U-shaped lever so that the assembling operation will take a relatively high amount of time whereby the total of manufacturing costs is increased.